Understanding the Nature of Aerobic Methane Emissions from Plants Grown under a Combination of Temperature, UVB Radiation and Watering Regime
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Methane (CH4) is an important greenhouse gas besides carbon dioxide, nitrous oxide, water vapour, ozone, and chlorofluorocarbons. The atmospheric concentration of CH4 has nearly tripled since pre-industrial times. It is the most abundant organic molecule in the Earth’s atmosphere and plays important roles in both the planet’s radiative energy budget and global atmospheric chemistry due to its global warming potential being up to 34 times as powerful as carbon dioxide. Methane production is mainly associated with methanogenesis under anoxic conditions. A decade ago, it was reported that plants produce CH4 under aerobic conditions by an unknown mechanism. Since then, many researchers have investigated the factors that influence CH4 emissions from plants. Methane emissions from plants may contribute significantly to the global CH4 budget. Most studies to date have examined the impact of single factors affecting plants, while the effects of multiple environmental factors and the interaction of abiotic stress factors on plants still need more exploration. In this thesis, pea (Pisum sativum) was used as a model species. Plants were grown in controlled-environment growth chambers under two temperature regimes (22/18°C and 28/24°C), two levels of ultraviolet-B radiation [0 (zero) and 5 (ambient) kJ m−2 d−1], and two watering regimes (well-watered and water-stressed). In pea, I have confirmed that environmental stress factors, such as higher temperatures, supplemental UVB radiation, or water stress, as individual factor or in combination, can increase aerobic CH4 emissions from plants. In addition, findings revealed interorgan and intrashoot variations in CH4 emissions from plants. Methane emissions were highest from stem and upper part of the shoot, as these were affected the most by stress factors. I also measured CH4 emissions from plants during vegetative and reproductive stages. In the vegetative stage, younger plants emitted more CH4 compared to older plants. Also, in the reproductive stage, CH4 emissions were higher from the younger pods than the older ones. In conclusion, the level of CH4 emissions varied with plant varieties and organs, as well as with plant vegetative and reproductive stages.